Sound reproducing machine



June 23, 1931. w. T. FORSE 1 SOUND REPRODUCING'MACHINE Filed Dec. 23, 1926 s Sheets-Sheet 2 my a - INVENTOR.

MZZz'a/n Tia/n asj'zis'e BYZ Z a Z ATTORNEY.

June 23, 1931. w, FQRSE 1,810,955

SOUND REPRODUCING MACHINE Filed Dec. 23, 1926' 3 Sheets-Sheet 3 I I N V EN TOR. Mllz'am Thomas F'orse ATTORNEY.

' Patented June 23, 1931 UNITED "STATES PATENT OFFICE WILLIAM THOMAS FORSE, OF LONDON, ENGLAND, ASSIGNOR TO COLUMBIA PHONO- GRAPH COMPANY, INC., OF BBIDGEPOR'I, CONNECTIGUI, A CORPORATION OF NEW YORK I SOUND REPRODUCING MACHINE I Application filed December 23, 1926, Serial No. 156,599, and in Great Britain February 26, 1926.

This invention relates to phonographs and other sound-reproducing machines and instruments with particular reference to the construction of the amplifying horn or chamher forming part thereof, the object of the invention being to provide a horn which shall be capable of giving increased volume of sound and a more uniform amplification throughout the range of musical frequencies,

while at the same time the construction employed shall be of such a compact nature that the improved horn may be located within substantially the same sized cabinet or receptacle as that provided for the usual types of horn.

It is well known in the art that in order to obtain as perfect reproduction as possible over a wide range of musical frequencies it is necessary to employ a sound conduit of increased length as compared with those of usual construction, and that the diameter and shape also influence the quality of the reproduction obtained, and in the specification of my prior British Patent No. 215,976, I have v laid down certain rules to be followed in providing the best amplifying area throughout the length of the horn for securing the most perfect reproduction. r

The present invention is based upon the observation that in order to secure the most efii-- cient results as regards uniformity of amplification for all ranges ofmusical frequencies there should be a definite-relation of length to sectional area (as distinguished from total 7 amplifying area) and in those cases Where" the sectional area of the sound conduit should is not in itself new in sound-reproducing machine construction.

The invention consists in a horn for a sound-reproducing machine or instrument which tapers progressively from its inlet end to a point about two-thirds of its total length so that the sectional area at this latter point does not exceed the value given by the formula where a is the diameter in inches at the inlet end of the horn c is the area in squareinches of the outlet end of the born 1 is an integer representing the length of horn in inches, and i 2'. equals where p is thc maximum frequency of the sound which can be effectively reproduced.

The invention also consists in a horn for a v one of a series of units in its length for approximately half of the total length, that is for the length of the inner or curved part of vthe horn, should correspond substantially with the equation I 2 Area .785( (n+2) where 0 is the diameter at the point of junction with the tone arm and a is any whole number of units of length from O to 8 commencing from a.

For a length of the continuation part of p 2 V 2 Area 785( b) where b is the diameter at the point of juncture with the first half of the horn, as determined by the above equation and m is any whole number of units of length from 0 to 7 commencing from Z1.

For approximately one-tenth of the total length at the outer end of the horn, it is flared or widened out to a suitable shape to fit the opening in the cabinet of the machine.

The invention also consists in other details and arrangements hereinafter described or indicated.

The accompanying drawings illustrate two modes of carrying out the invention.

Fig. l is an elevation partly in section of one form of amplifying horn constructed in accordance with the invention.

Fig. 2 is a half plan of the horn shown in Fig. 1.

Fig. 3 is a part sectional elevation of a phonograph cabinet with the horn of Fig. 1 arranged therein.

Fig. 45 is a plan of Fig. 1 with part broken away.

Fig. 5 is a perspective view of the horn shown in Fig. 4, and

Fig. 6 is a similar view to Fig. 5 but showing a slightly different form of horn.

In carrying my invention into effect, I so construct my improved amplifying horn that it tapers progressively from its inlet end to a point about two-thirds of its total length so that the sectional area at this latter point does not exceed the value given by the formula, above-referred to, namely In construction such born, the diameter of the inlet end of the horn will usually be de termined by constructional features of the machine or instrument in connection with which it is to be employed and the total length may be determined from the formula where v .is the velocity of sound in inches per section (that is, 13,200) and f is the lowest frequency in the range of musical frequencies which can be effectively reproduced. Thus, with a low frequency value of 85.6 per second, the length of the horn would be inches, and the diameter of the inlet end of the horn may be .75 inch while the area of the outlet end would in general be determined by the cabinet or other structural features of the machine, and may be taken as 101.5 square inches (that is, the outlet end would be 14 inches in one dimension, and 7 inches in the other). If now I denote the sectional area of the horn at a point two-thirds of its length from the inlet end by h, I have so that for the dimensions given above and seuors- .565

h .75 3.75 square inches.

Therefore, with the particular horn chosen of length 39 inches, inlet diameter .75 inch and outlet area 101.5 square inches, the sectional area. at a point approximately 26 inches from the inlet end will be 3.75 square inches, that is, the dimension in one direction may, for example, be 2 inches and in the other 1 inches. It will, however, be found from the rules given in the British patent already referred to, that the total amplifying area at this point in the length of the horn should be more than. double the sec tional area above given, and I, therefore, arrange to divide my horn into two branches, channels or conduits, each of which follows the formula given for cross-sectional area in relation to length while the two added to gether will give the approximate total amplifying area required at each point in the length of the horn. For this purpose, I construct the horn in such a way that the sound passage extends from its connection to the tone-arm (which may be of the usual swivel or other type) by a single tubular passage which slowly tapers outwards until it reaches a position where the sectional area approaches the limit for amplifying area and at this point the sound passage is then divided into two tubular passages, each having a sectional area equal to approximately one half the total amplifying area required, the two passages continuing to taper so that the sectional area is gradually enlarged in accordance with the formula hereinbefore given and each terminating in an outlet end, the area of which is one-half the total outlet area required for the amplifying horn and corresponding to the value of 0. By this means the horn provides for a continuous and steady increase in the amplifying area tapering from the inlet end to a point about two-thirds of its length from such end at which point the horn may then be joined to the flared outlet forming the last third of the length of the horn. and which may be shaped to suit the cabinet to which the horn is to be fitted.

In the accompanying drawings, Figs. 1 and 2 represent to scale one form of horn constructed in accordance with the foregoing de scription, the diameter at 20 being .75 inch, the combined outlet areas of the two horn portions at 21 being 101.5 square inches, and

the length of the horn from inlet to outlet end being 39 inches, while the sectional area at 22 (being a point 26 inches from the inlet end) is 3.75 square inches, and the flared portion of the horn at the outer end bein indicated at 23.

In the particular construction thus illustrated, the first part of the horn from the inlet end consists of a single tapered tube 24 of approximately square cross-section rounded at the inlet end and connected to the tonearm supporting pedestal from which it is curved downwards in a forward direction as clearly shown in Fig. 3. At its end this common conduit 24 divides into two sections 25, 26, each having an area at its inlet end equal to approximately one-half the area of the outlet end of the part 24, the parts 25, 26 being curved outwards and backwards as clearly shown in Figs. 4 and 5, and then being again bent in opposite directions and forwards, as shown at 27 and 28 and being connected at 22 to the flared portions 23 which run to the front of the cabinet and which open to a suitable flare so that the flared portions are juxtaposed along one edge as at 29 in order that they may fully occupy the sound outlet in the front of the cabinet, and it will be seen that the reverse direction bends in the sound conduits are arranged to lie in a similar plane.

The horn is, preferably, constructed in lead-covered iron sheet, but zinc or any other material may be employed for the purpose,

and it is sometimes an advantage to make one of the limbs or branches of the horn of a slightly greater capacity than the other for the purpose of eliminating objectionable resonance effects. It is also considered an advantage to deposit a coating of a celluloid or other form of paint or varnish on the horn for a similar purpose. I

The horn shown in Figs. 3, 4 and 5 is for a centrally mounted tone-arm but when the tone-arm is required to be mounted on one corner of the cabinet, a horn such as shown in Fig. 6 may be employed. In some cases when a longer horn is required for large cabinets, the single sound passage 24 may run vertically downwards where it then divides into two passages, as described above, such passages then being directed upwards towards the inlet and then curved forwardly at approximately right angles to the inlet passage where they fiare out and join each other to occupy the whole of the horn outlet in the front of the cabinet, the horn being preferably situated below the chamber containing the phonograph motor, and in such case the space below the horn outlet may be employed for the storage of records if desired. In some cases, also, the meeting edge 29 of the two flared portions of the horn or twohorn portions may be set back somewhat in relation to the outer edges so as to permit of the employment of louvres or sound-regulating dampers or devices adapted to be retatable about horizontal or. vertical axes without any liability for such to come into contact with the horn portions and without It will, however, be understood that the foregoing details of construction are given purely by way of illustration and not of 5 limitation, since I may modify the relative .dimensions of the horn while keeping within the limits of the formula hereinbefore, given, and may introduce variations into the form and section at various parts of the horn to suit the special requirements of various sound-boxes and cabinets or other structures or devices in connection with which the improved horn may be employed.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. horn for sound reproducing apparatus which tapers progressively from its inlet end to a point about two-thirds of its total length so that the sectional area of this latter point does not exceed the value given by the formula where a is the diameter in inches at the inlet end of the horn c is the area in square inches of the outlet end of the horn l is an integer representing the length of horn in inches, and

as equals where p is the maximum frequency of the sound which can be effectively reproduced.

2. A horn for sound-reproducingapparatus formed with branches each of which folv lows'the formula according to claim 1.

3. A horn for sound-reproducing machines having at its inlet end a common sound passage which then divides into oppositely directed sound passages running back towards the inlet end, which passages are subsequently oppositely bent back upon themselves in the same plane and terminate in flared ends which lie remote from the. inlet end, said passages being maintained separate from each other so as to maintain the sound divided during its entire passage through the horn.

4. A horn according to claim 1, having a number of coplanar reversed bends in its length.

5. In a sound amplifying horn, a forwardly curved inlet section, sections disposed the first mentioned sections have their outer sides substantially enclosed by the said other sections.

(3. A horn for sound reproducing apparatus formed with two branches each of which follows the formula according to claim 1, said horn having a number of coplanar reverse bends in its length, each of said branches having flared ends, and said flared ends being joined together along adjacent edges.

7. A horn for sound reproducing apparatus formed with two branches each of which follows the formula according to claim 1, said horn having a number of coplanar bends, each of said branches having a flared end, and said flared ends being joined together along adjacent edges, said joint for the adjacent edges of said ends being set back somewhat in relation to the outer edges of the flared ends.

8. In a sound amplifier, a forwardly curved tube providing an inlet section, a pair of tubes communicating with said inlet section to receive sound therefrom, said tubes running rearwardly at each side of said inlet section and having their rear ends reversedly bent in the plane of their major portion with their rear ends projecting forwardly, and independent outlet sect-ions connected with said ends of said intermediate sections, said outlet sections running forwardly of said intermediate sections and curving laterally toward each other to close the space between the outlet ends.

Signed at London, England, this 2nd of December, 1.926.

\VILLIAM THOMAS FOR-SE day 

